1. Field of the Invention
The present invention relates to a mechanism for DC level redistribution, and more particularly, to a method and an apparatus of DC level redistribution for saving pins by mixing two kinds of DC level redistributions.
2. Description of the Prior Art
Display system chips, such as televisions and liquid crystal display (LCD) screens, usually have an analog front-end circuit for converting analog signals (such as R, G, and B) into digital signals for displaying images. In practice, the analog signals are usually single-ended signals. But for noise considerations, the display system chip will adopt differential signals in signal processing, and thus the received single-ended signals must be converted into differential signals within the chip. Because the DC level of each signal is different from each other, AC-coupling techniques are used to input AC components of the signals into the display system chip. And then the DC level of each signal is redistributed after AC coupling capacitors.
Common approaches of the DC level redistribution, taking the DC level redistribution of image signals as an example, can be divided into two categories: a first approach is to first fix the DC levels of negative signals (e.g. R−, G−, and B−) of differential signals, and then fine-tune the DC levels of positive signals (e.g. R+, G+, and B+) of the differential signals; and a second approach is to first fix the DC levels of the positive signals of the differential signals, and then fine-tune the DC levels of the negative signals of the differential signals. The first approach has the advantage of sharing negative pins, but its disadvantage is that the voltage levels of the positive signals cannot be fixed at their assigned absolute voltages. However, the second approach allows the voltage levels of the positive signals to be fixed at their assigned absolute voltages, but separate negative pins are required, which is not allowed for a highly integrated display chip.